Hydraulic head closure mechanism

ABSTRACT

In order to reduce the time required for removal and replacement of a reactor vessel closure head, previously used studs for securing the closure head are replaced with a reduced member of larger diameter bolts located in radial slots in vessel and head flanges. All bolts are provided with individual hydraulic tensioning and tilting devices mounted on the head flange. The devices are operated simultaneously to preload the bolts and to actuate the bolts and the devices to an inclined position to permit the head to be removed when the tension load on the bolts is released.

United States Patent 1 Frisch, deceased et al.

[ Sept. 24, 1974 1 HYDRAULIC HEAD CLOSURE MECHANISM [73] Assignee:Westinghouse Electric Corporation,

Pittsburgh, Pa.

22 Filed: July 8, 1970 21 Appl. No.: 53,198

[52] US. Cl. 292/256.75, 85/1 T, 176/87,

220/55 D [51] Int. Cl Bd 45/30 [58] Field of Search 292/256.75, 256.73,256,

292/2565; 176/87; 220/55 D, 55 E, 55 F, 3; 52/223; 85/1 T, 32 T, 58 T;/175 [56] References Cited UNITED STATES PATENTS 2,734,824 2/1956 DeLuca 220/55 E 2,844,021 7/1958 Bryant 70/175 3,027,993 4/1962 Sommer292/256.75 X 3,130,628 4/1964 Blinn /1 T 3,154,006 10/1964 Novak 52/223R X 3,270,906 9/1966 Christensen 220/3 FOREIGN PATENTS OR APPLICATIONS135,079 3/1960 U.S.S.R. 220/55 E Primary Examiner-Robert L. WolfeAttorney, Agent, or Firm-J. R. Campbell [57] ABSTRACT In order to reducethe time required for removal and replacement of a reactor vesselclosure head, previously used studs for securing the closure head arereplaced with a reduced member of larger diameter bolts located inradial slots in vessel and head flanges. All bolts are provided withindividual hydraulic tensioning and tilting devices mounted on the headflange. The devices are operated simultaneously to preload the bolts andto actuate the bolts and the devices to an inclined position to permitthe head to be removed when the tension load on the bolts is released.

15 Claims, 5 Drawing Figures PAINTED-89241974 3.831; 694

sow ans 5 1 HYDRAULIC HEAD CLOSURE MECHANISM CROSS REFERENCE TO RELATEDAPPLICATIONS This application relates to the following applicationsconcurrently filed herewith:

Ser. No. 53,207 entitled Means for Rapidly Exposing the Core of ANuclear Reactor For Refueling by Erling Frisch and Harry N. Andrews.

Ser. No. 53,203 entitled Cable Support Structure For Enabling A NuclearReactor To Be Refueled Rapidly By Erling Frisch and Harry N. Andrews.

Ser. No. 53,201 entitled Rapidly Refuelable Nuclear Reactor by ErlingFrisch and Harry N. Andrews.

Ser. No. 53,200 entitled Combination of Nuclear Reactor and MissileShield by Erling Frisch and Harry N. Andrews.

Ser. No. 53,199 entitled Means for Retaining and Handling Reactor O-RingSeals by Erling Frisch.

Ser. No. 53,202 entitled Rapidly Refuelable Nuclear Reactor by Harry N.Andrews and Richard S. Orr.

BACKGROUND OF THE INVENTION This invention relates generally, topressure vessels and, more particularly, to mechanism for securing andreleasing the closure heads for nuclear reactor vessels.

Heretofore, the closure heads of large pressurized power reactors havebeen secured to the pressure vessel by a large number of studs which arethreaded into the vessel flange and extend through holes in the headflange. The necessary loading on this flange is obtained by nuts on theupper threaded portion of the studs which are tightened .by hand whilethe studs are preloaded by hydraulic tensioning devices. Threetensioners are usually provided for each plant. They are applied to thestuds in a certain prearranged rotation until all studs carryapproximately the same load. To achieve this, each stud must betensioned at least twice.

To remove the closure head, the studs must be tensioned until the nutsbecome unloaded and can be backed off. Following this, all nuts andstuds must be removed and stored before the closure head can be liftedoff and refueling can commence.

In view of the large number of studs, for example 56, utilized in alarge reactor vessel, it is easily realized that considerable time, forexample 72 hours, is required for removing the closure head aftershutdown and replacing it after refueling if there are no complications.Also, the use of threaded studs, which must be completely removed foreach refueling, is considered unsatisfactory since galling of thethreads, which is a distinct possibility and actually has occurred onseveral occasions, will seriously affect the refueling schedule. Sincethe cost of shutdown of a large plant is approximately 55 l00,000 perday, there is a need for reducing the time requirement for refueling andalso for avoiding the use of studs.

SUMMARY OF THE INVENTION In accordance with the present invention, thelarge number of holding studs for securing a closure head on a reactorvessel is replaced with a smaller number of larger diameter bolts,located in radial slots in the flanges of the vessel and the closurehead, and all bolts are provided with individual hydraulic tensioningdevices which are permanently located on the head flange. The heads ofthe bolts engage the bottom surface of the vessel flange and each boltextends continuously through its tensioning device. To permit the boltheads to clear the vessel flange while lifting the enclosure head, atilting device is provided for each bolt which actuates the bolt and itstensioning device to an inclined position during this operation. Byenergizing all tensioning devices simultaneously and all tilting devicessimultaneously, the time required for head removal and replacementduring re-fueling can be reduced to a few hours.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of thenature of the invention, reference may be had to the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich:

FIGS. 1A and 1B, when joined end-to-end, constitute a sectional viewthrough a portion of a reactor vessel and closure head and one of theholding bolts and its tensioning and tilting devices;

FIG. 2 is a view, in section, taken along the line IIII of FIG. 18;

FIG. 3 is a view, in plan, of the tensioning and the tilting devices;and

FIG. 4 is an enlarged detail view of a coupling utilized in thehydraulic system for the devices.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings,particularly to FIGS. 1A and 1B, the structure shown therein comprises aportion of a generally cylindrical reactor vessel 10 having an integraloutwardly extending flange 11, and ,agenerally hemispherical closurehead 12 having an integral outwardly extending flange 13 which mateswith the flange 11 on the vessel 10. The vessel 10 may be of a type,well known in the art, suitable for use .in a nuclear power system.

As shown more clearly in FIG. 2, a plurality of vertically alignedradial slots 15 is provided in the peripheries of the flanges l1 and 13.In order to retain the closure head 12 on the vessel 10, holding bolts16 are disposed in the radial slots 15. Each bolt 16 has a head 17engaging the bottom surface 18 of the vessel flange 11.

As shown more clearly in FIG. IA, each bolt 16 extends continuouslyupwardly through a hydraulic pressure tensioning device 21 whichsurrounds the upper portion of the bolt 16 and is mounted on the upperor top surface 22 of the closure head flange 13. Each bolt 16 has athreaded portion 23 at its upper end which extends above the top of thetensioning device 21. Each tensioning device 21 is positioned on theflange 13 by means of one or more positioning pins 24 with tapered upperends which enter holes 25 in a base plate 26 of the device 21, and by aninclined front surface of a bracket 27 which supports a tilting device28. The bracket 27 may be attached to the top surface of the flange 13by means of bolts 29.

In order to obtain space for the individual tensioning devices 21, thenumber of holding bolts 16 has been reduced to 28 which is one-half thenumber of bolts previously utilized with a reactor vessel of the samesize. The diameter of the present bolts is 10 inches, whereas thediameter of the prior bolts is 7 inches. Each bolt 16 is approximately140 inches long and the preloading will be approximately 2,500,000 lbs.per bolt for a pressure vessel having an inside diameter of 173 inches.

In order to obtain the required bolt loading without exceeding ahydraulic fluid pressure of 10,000 psi, the tensioning device 21 isprovided with two pistons 31 and 32 in tandem. The pistons 31 and 32 arereciprocably disposed inside cylinders 33 and 34, respectively,supported between the base plate 26 and a top plate 36 of a generallyrectangular shape (see FIG. 3) whice are held together by four tie rods37. The lower cylinder 34 has a base portion 38 which rests on the baseplate 26, and the upper cylinder 33 has a base portion 39 which rests onthe top of the cylinder 34. A collar 41 is disposed between the top ofthe upper cylinder 33 and the top plate 36.

The hydraulic fluid is introduced under the piston 31 through relativelysmall diameter tubing 42 which enters the wall of the cylinder 33through a bolted flanged coupling 43 having a metal O-ring seal 44 asshown in detail in FIG. 4. The hydraulic flows from the cylinder 33 intothe cylinder 34 through a metal tube 45 and couplings 43. Similarcouplings 43 are also provided in the hydraulic lines near the top ofthe tensioning devices to permit ease of disassembly when it becomesnecessary to remove the device for inspection or repair. The lines fromthese couplings to hydraulic manifolds 46, which conveniently may bemounted on an existing structure (not shown) above the tensioningdevices, must be flexible to permit tilting of the tensioning devicesand the holding bolts, as will be described more fully hereinafter. Theflexibility may be achieved by forming this part of the tubing into aloose helical spring 47.

Hydraulic pressure may also be applied above the upper piston 31 todrive both pistons downwardly against any residual pressure under thepistons resulting from a possible stand pipe effect of the pressurizingequipment. In this manner the bolt 16 is permitted to drop downwardly bygravity under certain conditions described hereinafter.

As shown, the tilting device 28 is of the fluid pressure actuated type.It comprises a reciprocating piston 51 disposed inside a cylinder 52held between a base plate 53 and a top plate 54 by tie rods 55.Hydraulic or other pressure fluid is introduced above the piston 51through a passageway 56 in the top plate 54 and a coupling 43 of thetype previously described. The piston 51 is connected to a bifurcatedmember 57 by means of a connecting rod 58 which is threaded into thepiston 51 and the member 57. The member 57 has arms 59 which straddle alever 61 secured to or formed integrally with the top plate 36 of thetensioning device 21. A cross pin 62 in the arms 59 engages the lever 61when the piston 51 is moved downwardly.

In the drawing, the pistons in the tensioning device 21 are shown in aposition where hydraulic pressure is being applied under the pistons fortensioning the bolt 16. The developed upward thrust is transmittedthrough a set of spherical washers 63 to thrust means 64 fixed on thebolt 16. The thrust means 64 may be a nut threaded on the bolt 16 andfixed in positions by means of a screw 65. Other suitable thrusttransmitting means affixed to the bolt 16 may be utilized if desired.

When the desired tension is reached, adjustable means, preferably a nut66 which is free to turn on the threads 23 on the bolt 16 above thetensioning device 21, is lowered by means of handwheel 67 until the nut66 is in firm contact with the top support plate 36 through another setof spherical washers 68. The handwheel 67 may be attached to theadjustable nut 66 by means of bolts 69.

When the hydraulic pressure is subsequently removed from the tensioningdevice 21, the bolt tension load will be transferred from the thrustmeans 64 to the adjustable nut 66, and the tension load is transmittedthrough the cylinders and other stationary parts of the tensioningdevice, which are under compression, to the closure head flange 13. Inthis manner the tension load is transferred from the fixed nut 64, whichis inside the tensioning device and not readily accessible, to theadjustable nut 66 which is outside the tensioning device and readilyaccessible for manual operation.

The actual value of the bolt loading can be estimated by a micrometer 70on top of the bolt 16 which indirectly measures the elongation or strainof the stressed bolt by comparing its length with that of an unstressedrod 71 of the same material, located in a hole through the center of thebolt and attached to the bolt head 17.

In preparation for removing the closure head 12 for refueling, hydraulicpressure is again applied under the pistons in the tensioning device 21until the load is completely transferred to the fixed nut 64. This freesthe adjustable nut 66 which is subsequently backed off by hand until itreaches its top position as determined by a fixed stop nut 72 on thethreaded portion 23 of the bolt 16. The nut 72 may be fixed on the bolt16 by means of a screw 74.

The pressure under the pistons 31 and 32 is then removed and pressure isapplied above the piston 31 through a passageway 73 in the collar 41 anda coupling 43 attached to the collar. This causes unloading and loweringof the bolt 16 until it assumes its lowest position as indicated by thedot-dash lines of the bolt head 17. With all bolts in this position,pressure is applied above the piston 51 of the tilting device 28. Thiscauses a downward pressure to be applied to the outer end of the lever61 on each of the tensioning devices, thereby actuating the tensioningdevice and the bolts 16 from their vertical position to an inclinedposition as indicated by the dot-dash lines in FIGS. 1A and 1B. Thedownward force on the lever 61 causes the device 21 to pivot about apivot line 75 located at the inner corner of the base plate 26 where itabuts the bracket 27 which supports the tilting device 28. The taperedend of the pin 24 and the inclined surface of the bracket 27 permit thetensioning device 21 to tilt about the pivot line 75.

An extension on the bottom of the tilting device piston 51 stops pistonmovement downwardly when the desired tilting position has been reached.Rotation of the bifurcated member 57 is prevented by an upwardlyextending projection 76 on the top plate 54 of the tilting device 28.

With all holding bolts 16 tilted or inclined, the closure head 12 may belifted vertically without interference of the bolts with the pressurevessel flange 11. Any time after the bolt heads clear the flange,pressure on the tilting devices may be removed causing the bolts toreturn to the vertical position. A heavy spring 77 in the cylinder 52 ofthe tilting device returns the piston 51 to its original position afterthe pressure is removed.

In order that the tilting device 28 can follow the tilting movement ofthe tensioning device 21, the base plate 53 of the tilting device ismounted on a swivel pin 78 supported on a lower support base 79 attachedto the bracket 27 by bolts 81. A spring 82 is provided between the lowersupport base 79 and the actuator base plate 53 to return the tiltingdevice 28 to the vertical position when the pressure is removed from thepiston 51, thereby deenergizing the tilting device.

Each tensioning device 21 may be removed individually for inspection orrepair by first disconnecting the hydraulic supply lines and thenforcing the tilting device 28 out of the way. The tensioning device 21may be lifted vertically until clearing the positioning pins 25 and thenradially until the bolt heads clear the vessel flange.

From the foregoing description, it is apparent that the inventionprovides a head closure mechanism which enables the time required forhead removal and replacement during refueling of a nuclear reactor to begreatly reduced. The tensioning devices and the tilting devices of themechanism may be readily mounted on the top flange of the closure headof the reactor vessel. During normal operation of a reactor, the bolttension load is transmitted to the closure head flange through membersof the tensioning devices which are under compression. This increasesthe effective length of the holding bolts, thereby preventing anyappreciable change in bolt loading resulting from differential thermalexpansion.

What we claim is:

1. A head closure mechanism for a nuclear reactor comprising: agenerally cylindrical reactor vessel and a closure head each having anoutwardly extending flange with a plurality of vertically aligned radialslots in the periphery of the flanges, bolts disposed in said slots toretain the closure head on the vessel, each bolt having a head engagingthe bottom surface of the vessel flange, a hydraulic pressure bolttensioning device surrounding each bolt and mounted on the top surfaceof the closure head flange, said bolt extending continuously through thedevice with a threaded portion at its upper end, thrust means fixed onthe bolt axially outward from the tensioning device, said tensioningdevice being located between the thrust means and the head flange, saidtensioning device applying force in one axial direction against the headflange and in the other axial direction against the thrust means on thebolt for elongating the bolt between the bottom of the vessel flange andsaid thrust means on the bolt, and adjustable means threaded on thethreaded portion axially outward from the tensioning device and thethrust means for maintaining the bolt under tension when the hydraulicpressure is removed from the tensioning device.

2. The mechanism defined in claim 1, wherein the adjustable means ismovable into contact with the tensioning device when the bolt iselongated to transfer the tension load on the bolt from the fixed thrustmeans to the adjustable means when the hydraulic pressure is removed.

3. The mechanism defined in claim 1, wherein the tensioning deviceincludes at least one cylinder containing a reciprocable piston forapplying a tension load on the bolt through said fixed thrust means, andthe adjustable means is operable movable to a position in which thetension load on the bolt is transmitted to the closure head flangethrough the adjustable means and the cylinder when the hydraulicpressure is removed from the piston.

4. The mechanism defined in claim 1, wherein the tensioning deviceincludes a base plate mounted on the top surface of the closure headflange, a top plate spaced from the base plate, at least one cylinderdisposed between the plates, a reciprocable piston within the cylinderfor applying a tension load on the bolt through said thrust means whenhydraulic pressure is applied to the piston, and said adjustable meansbeing operable to a position with respect to the top plate to transferthe tension load on the bolt from the thrust means to the adjustablemeans and transmit the bolt tension load through the top plate and thecylinder and the base plate to the closure head flange when thehydraulic pressure is removed from the piston.

5. The mechanism defined in claim 1, wherein the thrust means includes anut affixed on the bolt substantially at the top of the tensioningdevice, and the adjustable means includes a nut having a handwheelattached thereto for manually rotating the nut.

6. The mechanism defined in claim 1, wherein the tensioning device isoperable to permit disengagement of the bolt head from the vesselflange, and including a tilting device mounted on the closure headflange for actuating the bolt and its tensioning device to an inclinedposition to permit the closure head to be lifted vertically without thebolt interferring with the vessel flange.

7. The mechanism defined in claim 6 wherein the tensioning device andthe bolt are actuated about a pivot line on the top surface of theclosure head flange.

8. The mechanism defined in claim 7, including a lever on the tensioningdevice engaged by the tilting device to actuate the tensioning deviceand the bolt about the pivot line.

9. The mechanism defined in claim 8, including a swivel support for thetilting device permitting it to move to an inclined position when thetensioning device and the bolt are actuated to the inclined position.

10. The mechanism defined in claim 9, including spring means forreturning the tilting device to a vertical position when the tiltingdevice is deenergized.

11. The mechanism defined in claim 8, wherein the tilting devicecomprises a fluid pressure actuated piston, a bifurcated member havingarms straddling said lever, and a cross pin in the arms engaging thelever when the piston is actuated downwardly.

12. The mechanism defined in claim 11, including a spring for returningthe piston to its original position when fluid pressure is released fromthe piston.

13. A head closure mechanism for a vessel member and a closure headmember each having an outwardly extending flange with a plurality ofvertically aligned openings therein, comprising bolts disposed in saidopenings to retain the closure head member on the vessel member, ahydraulic pressure tensioning device surrounding each bolt and mountedon a surface of the flange on one of said members, said bolt extendingcontinuously through the device with a threaded portion at one end,thrust means fixed on the bolt, said tensioning device applying forcebetween the thrust means and tension load on the bolt from the fixedthrust means to the adjustable means when the hydraulic pressure isremoved.

15. The mechanism defined in claim 14, wherein the tension load on thebolt is transmitted to the flange on one of said members through theadjustable means and the tensioning device when the hydraulic pressureis re-

1. A head closure mechanism for a nuclear reactor comprising: agenerally cylindrical reactor vessel and a closure head each having anoutwardly extending flange with a plurality of vertically aligned radialslots in the periphery of the flanges, bolts disposed in said slots toretain the closure head on the vessel, each bolt having a head engagingthe bottom surface of the vessel flange, a hydraulic pressure bolttensioning device surrounding each bolt and mounted on the top surfaceof the closure head flange, said bolt extending continuously through thedevice with a threaded portion at its upper end, thrust means fixed onthe bolt axially outward from the tensioning device, said tensioningdevice being located between the thrust means and the head flange, saidtensioning device applying force in one axial direction against the headflange and in the other axial direction against the thrust means on thebolt for elongating the bolt between the bottom of the vessel flange andsaid thrust means on the bolt, and adjustable means threaded on thethreaded portion axially outward from the tensioning device and thethrust means for maintaining the bolt under tension when the hydraulicpressure is removed from the tensioning device.
 2. The mechanism definedin claim 1, wherein the adjustable means is movable into contact withthe tensioning device when the bolt is elongated to transfer the tensionload on the bolt from the fixed thrust means to the adjustable meanswhen the hydraulic pressure is removed.
 3. The mechanism defined inclaim 1, wherein the tensioning device includes at least one cylindercontaining a reciprocable piston for applying a tension load on the boltthrough said fixed thrust means, and the adjustable means is operablemovable to a position in which the tension load on the bolt istransmitted to the closure head flange through the adjustable means andthe cylinder when the hydraulic pressure is removed from the piston. 4.The mechanism defined in claim 1, wherein the tensioning device includesa base plate mounted on the top surface of the closure head flange, atop plate spaced from the base plate, at least one cylinder disposedbetween the plates, a reciprocable piston within the cylinder forapplying a tension load on the bolt through said thrust means whenhydraulic pressure is applied to the piston, and said adjustable meansbeing operable to a position with respect to the top plate to transferthe tension load on the bolt from the thrust means to the adjustablemeans and transmit the bolt tension load through the top plate and thecylinder and the base plate to the closure head flange when thehydraulic pressure is removed from the piston.
 5. The mechanism definedin claim 1, wherein the thrust means includes a nut affixed on the boltsubstantially at the top of the tensioning device, and the adjustablemeans includes a nut having a handwheel attached thereto for manuallyrotating the nut.
 6. The mechanism defined in claim 1, wherein thetensioning device is operable to permit disengagement of the bolt headfrom the vessel flange, and including a tilting device mounted on theclosure head flange for actuating the bolt and its tensioning device toan inclined position to permit the closure head to be lifted verticallywithout the bolt interferring with the vessel flange.
 7. The mechanismdefined in claim 6 wherein the tensioning device and the bolt areactuated about a pivot line on the top surface of the closure headflange.
 8. The mechanism defined in claim 7, including a lever on thetensioning device engaged by the tilting device to actuate thetensioning device and the bolt abouT the pivot line.
 9. The mechanismdefined in claim 8, including a swivel support for the tilting devicepermitting it to move to an inclined position when the tensioning deviceand the bolt are actuated to the inclined position.
 10. The mechanismdefined in claim 9, including spring means for returning the tiltingdevice to a vertical position when the tilting device is deenergized.11. The mechanism defined in claim 8, wherein the tilting devicecomprises a fluid pressure actuated piston, a bifurcated member havingarms straddling said lever, and a cross pin in the arms engaging thelever when the piston is actuated downwardly.
 12. The mechanism definedin claim 11, including a spring for returning the piston to its originalposition when fluid pressure is released from the piston.
 13. A headclosure mechanism for a vessel member and a closure head member eachhaving an outwardly extending flange with a plurality of verticallyaligned openings therein, comprising bolts disposed in said openings toretain the closure head member on the vessel member, a hydraulicpressure tensioning device surrounding each bolt and mounted on asurface of the flange on one of said members, said bolt extendingcontinuously through the device with a threaded portion at one end,thrust means fixed on the bolt, said tensioning device applying forcebetween the thrust means and said flange for tensioning the bolt, andadjustable means threaded on said threaded portion axially outward ofthe tensioning device for maintaining the bolt under tension when thehydraulic pressure is removed from the tensioning device.
 14. Themechanism defined in claim 13, wherein the thrust means is mounted onthe bolt internally of the tensioning device, and the adjustable meansis movable into contact with the tensioning device to transfer thetension load on the bolt from the fixed thrust means to the adjustablemeans when the hydraulic pressure is removed.
 15. The mechanism definedin claim 14, wherein the tension load on the bolt is transmitted to theflange on one of said members through the adjustable means and thetensioning device when the hydraulic pressure is removed.